1. Field of the Invention:
The present invention relates to novel organopolysiloxane compositions containing a "latent" tin catalyst that are capable of being crosslinked into elastomeric state, for example, in thin layer form.
2. Description of the Prior Art:
Curable organopolysiloxane compositions are well known to this art that crosslink in the presence of a tin or platinum (C) catalyst by a polycondensation reaction between a polydiorganosiloxane (A) having silanol end groups and a polydiorganosiloxane (B) containing at least three SiH (silicon hydride) groups per molecule.
These compositions, generally free from inorganic fillers, can be used for producing a non-adhesive and/or water-repellent elastomeric coating on various substrates (supports), in particular on paper and on films made of a plastic material, such as polyolefin, polyester, regenerated cellulose, or even metal or the like, with a view to depositing a silicone coating (thin layer), the thickness of which can range from approximately 1 .mu.m to a few mm.
The known industrial compositions can be divided into three basic groups:
(i) solvent-free compositions in which the polymers (A) and (B) are employed in bulk, namely, substantially without any organic solvent. Compositions of this type are described, in particular, in British Patents Nos. GB-A-1,374,792 and GB-A-1,504,716, where the catalyst (C) is a platinum compound. The mixture of the polymers (A) and (B) must then exhibit a viscosity of less than approximately 5000 mPa.s at 25.degree. C.;
(ii) the compositions in solution in an organic solvent, in which the polymers (A) and (B) may exhibit very high viscosities, which can improve the quality of the coating. The solvent is then removed by heating during the crosslinking. Such compositions containing a tin catalyst (C) are described, for example, in patents U.S. Pat. No. 3,061,567 and No. GB-A-1,504,716;
(iii) the aqueous emulsion compositions containing water and an emulsifying agent in addition to the three constituents (A), (B) and (C). The water is removed by heating during the crosslinking. Compositions of this type are described, for example, in U.S. Pat. Nos. 4,127,460, 4,288,356 and 4,624,900.
All of the known compositions of the aforementioned types exhibit the characteristic of being insufficiently stable over long-term storage. This is the reason the commercial forms thereof all exist as at least two components (or two packs) which the user mixes when required. After mixing, the composition has a pot life which typically is not longer than 48 hours.
It is quite apparent that such packaging in at least two packs constitutes a serious constraint both for the manufacturer and, above all, for the user of the composition.
Indeed, in conducting the mixing, the user, in particular, can make a mistake in measuring out and/or preparing too much mixture for his actual needs, resulting in a loss of product, which gels and therefore becomes unusable once the pot-life period has expired.